163 lines
5.0 KiB
Groff
163 lines
5.0 KiB
Groff
.\" Copyright (c) 1983, 1991, 1992, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)sigaltstack.2 8.2 (Berkeley) 5/1/95
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd May 6, 2010
|
|
.Dt SIGALTSTACK 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm sigaltstack
|
|
.Nd set and/or get signal stack context
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In signal.h
|
|
.Bd -literal
|
|
typedef struct {
|
|
char *ss_sp;
|
|
size_t ss_size;
|
|
int ss_flags;
|
|
} stack_t;
|
|
.Ed
|
|
.Ft int
|
|
.Fn sigaltstack "const stack_t * restrict ss" "stack_t * restrict oss"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn sigaltstack
|
|
system call
|
|
allows defining an alternate stack on which signals
|
|
are to be processed for the current thread.
|
|
If
|
|
.Fa ss
|
|
is non-zero,
|
|
it specifies a pointer to and the size of a
|
|
.Em "signal stack"
|
|
on which to deliver signals.
|
|
When a signal's action indicates its handler
|
|
should execute on the signal stack (specified with a
|
|
.Xr sigaction 2
|
|
system call), the system checks to see
|
|
if the thread is currently executing on that stack.
|
|
If the thread is not currently executing on the signal stack,
|
|
the system arranges a switch to the signal stack for the
|
|
duration of the signal handler's execution.
|
|
.Pp
|
|
An active stack cannot be modified.
|
|
.Pp
|
|
If
|
|
.Dv SS_DISABLE
|
|
is set in
|
|
.Fa ss_flags ,
|
|
.Fa ss_sp
|
|
and
|
|
.Fa ss_size
|
|
are ignored and the signal stack will be disabled.
|
|
A disabled stack will cause all signals to be
|
|
taken on the regular user stack.
|
|
If the stack is later re-enabled then all signals that were specified
|
|
to be processed on an alternate stack will resume doing so.
|
|
.Pp
|
|
If
|
|
.Fa oss
|
|
is non-zero, the current signal stack state is returned.
|
|
The
|
|
.Fa ss_flags
|
|
field will contain the value
|
|
.Dv SS_ONSTACK
|
|
if the thread is currently on a signal stack and
|
|
.Dv SS_DISABLE
|
|
if the signal stack is currently disabled.
|
|
.Sh NOTES
|
|
The value
|
|
.Dv SIGSTKSZ
|
|
is defined to be the number of bytes/chars that would be used to cover
|
|
the usual case when allocating an alternate stack area.
|
|
The following code fragment is typically used to allocate an alternate stack.
|
|
.Bd -literal -offset indent
|
|
if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
|
|
/* error return */
|
|
sigstk.ss_size = SIGSTKSZ;
|
|
sigstk.ss_flags = 0;
|
|
if (sigaltstack(&sigstk, NULL) < 0)
|
|
perror("sigaltstack");
|
|
.Ed
|
|
An alternative approach is provided for programs with signal handlers
|
|
that require a specific amount of stack space other than the default size.
|
|
The value
|
|
.Dv MINSIGSTKSZ
|
|
is defined to be the number of bytes/chars that is required by
|
|
the operating system to implement the alternate stack feature.
|
|
In computing an alternate stack size,
|
|
programs should add
|
|
.Dv MINSIGSTKSZ
|
|
to their stack requirements to allow for the operating system overhead.
|
|
.Pp
|
|
Signal stacks are automatically adjusted for the direction of stack
|
|
growth and alignment requirements.
|
|
Signal stacks may or may not be protected by the hardware and
|
|
are not ``grown'' automatically as is done for the normal stack.
|
|
If the stack overflows and this space is not protected
|
|
unpredictable results may occur.
|
|
.Sh RETURN VALUES
|
|
.Rv -std sigaltstack
|
|
.Sh ERRORS
|
|
The
|
|
.Fn sigaltstack
|
|
system call
|
|
will fail and the signal stack context will remain unchanged
|
|
if one of the following occurs.
|
|
.Bl -tag -width Er
|
|
.It Bq Er EFAULT
|
|
Either
|
|
.Fa ss
|
|
or
|
|
.Fa oss
|
|
points to memory that is not a valid part of the process
|
|
address space.
|
|
.It Bq Er EPERM
|
|
An attempt was made to modify an active stack.
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa ss_flags
|
|
field was invalid.
|
|
.It Bq Er ENOMEM
|
|
Size of alternate stack area is less than or equal to
|
|
.Dv MINSIGSTKSZ .
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr sigaction 2 ,
|
|
.Xr setjmp 3
|
|
.Sh HISTORY
|
|
The predecessor to
|
|
.Fn sigaltstack ,
|
|
the
|
|
.Fn sigstack
|
|
system call, appeared in
|
|
.Bx 4.2 .
|